Synthesis of diamonds by use of microwave plasma chemical-vapor deposition: Morphology and growth of diamond films

An investigation is made of the surface morphology and growth of polycrystalline diamond films deposited on Si substrates using the microwave plasma chemical-vapor-deposition (CVD) method. For the source gas, ${\mathrm{CH}}_4$ and ${\mathrm{H}}_2$ gases mixed in different concentrations are used. Scanning electron microscope pictures of the diamond films synthesized for 7 h show that the film surface consists of triangular (111) diamond faces for ${\mathrm{CH}}_4$ concentrations cc≃0.4 vol %. For c≳1.2 vol %, the number density of (100) faces decreases with c and finally at c≃1.6 vol % the film surface becomes entirely structureless, consisting of microcrystallites only. For characterization of the films, x-ray and electron diffraction are measured along with Raman and infrared spectra. In the study of the evolution of surface morphology during film growth, it is found that diamond particles grown on the substrate initially increase their size almost uniformly until the substrate is entirely covered. Then a secondary growth takes place, followed by surface-restructuring processes such as ‘‘fusion’’ and ‘‘absorption’’ among secondary crystallites. As a result, well-defined diamond faces are formed progressively on the film surface. Higher-order growths followed by the restructuring processes occur periodically as the CVD synthesis proceeds.